VESSEL DAVIT DESIGN (BASED ON PRESSURE VESSEL DESIGN MANUAL BY DENNIS R MOSS)
L2=1000
L1=2000
R=750 2000
M2
M1
Pipe Material : SA 106 GR. B Minimum Yield Stress, Sy = Allowable Bending Stress, Fb = Pipe = 6" Sch 120, OD = tp = thickness of pipe = di = ID of Pipe
=
r = Radius of Gyration A = Cross sectional Area a = Outside radius of pipe L1 L2 L3 L4 R B (Guide plate width)
I = Moment of Inertia of Pipe = Z= Section modulous of Pipe = WL= Maximum rated capacity = W1=Weight of boom & brace = WD = Total Weight of davit = Cv =
24579160 292087 500 125 350
mm4 mm3 Kgs Kgs Kgs
1.8
Ch
=
0.5
fv = Cv WL
=
900 Kgs
fh = Ch WL
=
250 Kgs
Axial load on davit mast, P: P =2fv + WD =
2150 Kgs 21092 N
Bending Moment in davit mast, M1 (TYPE 1): Type 1: M1 =2fvL1+0.5W1L1+fhL2 = For Type B Davit: Axial Stress: fa = P/A
3975000 Kgf - mm 38994750 N-mm
=
2.45 MPa
Bending Moment, M2: M2 = M1 (L2-R)/L2
9748688 N-mm
Coefficients: = tp R/a2 =
1.93 0.22 0.84
= 6 / (5+6 ) = K = 1 - 9 / (10+12) =
Bending Stress, fb : Sy, Yield Stress for SA 106 Gr. B is 241.32 MPa. Fb, Allowable bending Stress (0.6 x Sy) is 144.8 MPa. At M1, fb = M1/Z
133.50 MPa < Fb, Hence Safe
At M2, fb = (M2 a/I)*(2 / 3K Sqrt(3))
32.86 MPa
Combined Stress: Slenderness Ratio = 2.1*L2/r =
39
Fa = Allowable Axial Stress =
132.86 MPa
(From Table C-36 of Manual of Steel Construction by AISC) fa/Fa + fb/Fb = 0.94 <1.0, Hence Safe
FINDING EQUIVALENT RADIAL LOAD, Fre Radial Force At Guide & Support, Fr
=
M1/L3 38994.8 N
= Fr is max when davit rotation is at 0o Circumferential moment at guide and support, M = Fr * L4 M is max when davit rotation is at 90o, Longitudinal moment at guide, Mx=P*L4
11308478 N-mm 6116535 N-mm
Equivalent Unit load, w = (Fr*Cos/ B) + (6*Fr*L4*Sin / B2 )
